1. Technical Field of the Invention
The present invention relates generally to an in-vehicle power transmission device equipped with a plurality of power split rotors which work to split output power or torque among a rotary electric machine (e.g., a dynamo-electric machine), an internal combustion engine, and driven-wheels of a vehicle and are designed to rotate in conjunction with each other and a driving system for vehicles.
2. Background Art
In recent years, in terms of reducing the amount of energy consumed by automotive vehicles, so-called hybrid vehicles have been put into practical use which are equipped with a rotary electric machine such as an in-vehicle power source made up of an electric motor and a generator in addition to an internal combustion engine. The hybrid vehicles are typically controlled to stop the internal combustion engine in a low speed running range in view of the fact that the internal combustion engine is usually inefficient in energy use in the low speed running range. The hybrid vehicles are facing a difficulty in how to restart the internal combustion engine during running of the vehicles. For example, it is difficult to bring a rotor which is coupled with driven wheels of the vehicle and now rotating into mechanical connection with the crankshaft of the internal combustion engine which is at a stop.
In order to avoid the above problem, there have been in practice use hybrid vehicles equipped with the electric motor whose output shaft is connected directly to the crankshaft of the internal combustion engine to transmit the torque, as outputted from the electric motor, to the crankshaft of the engine to start it. After start-up of the engine, the torque, as produced by the engine, is transmitted to the driven wheels of the vehicle.
Additionally, there have been in practical use hybrid vehicles equipped with a typical planetary gear speed reducer (also called an epicycle reduction gear train) made up of three rotors: a sun gear, a carrier (also called a planetary carrier), and a ring gear to which the generator, the internal combustion engine, and the electric motor are coupled, respectively. The driven wheels of the vehicle are coupled mechanically to the electric motor. In operation, the torque is applied to the sun gear or the ring gear to rotate the carrier, thereby rotating the rotating shaft (i.e., the crankshaft) of the internal combustion engine. The internal combustion engine is started by using the torque of the carrier. After the start-up of the internal combustion engine, the engine torque is transmitted to the driven wheels of the vehicle through the carrier.
For example, typical hybrid vehicles are known in the following patent publications.    Japanese Patent Publication No. 3580257    Japanese Patent Publication No. 3626151    Japanese Patent Publication No. 3614409    Japanese Patent First Publication No. 2002-281607    Japanese Patent First Publication No. 2000-142146    Japanese Patent First Publication No. 9-46821    Japanese Patent First Publication No. 2006-77859
The direct coupling of the rotating shaft of the electric motor to that of the internal combustion engine, as described above, will cause the torque load, as produced by the internal combustion engine, to be exerted on the electric motor, thus resulting in an increase in consumed amount of energy. A problem is also encountered that when the internal combustion engine is started, the pulsation of torque occurring at the rotating shaft of the internal combustion engine may result in a decrease in driveability of the vehicle.
Further, the use of the planetary gear speed reducer leads to the problem that starting of the internal combustion engine when the rotational speed of the carrier is low will cause the internal combustion engine to be kept run at low speeds for a while. This is against the intended purpose of the hybrid vehicles to run the internal combustion engine in a speed range in which the efficiency in energy use is high.